Sinker electrode for Tungsten, Niobium, refractories etc

[claya]

Can someone suggest electrode options for the refractory materials? Someone recommended Copper but which copper (P ure, C110 or C145 Tellurium)?

Current projects are Tungsten and Niobium. Pure copper (C101) is wearing faster than expected.

The electrodes are VERY small 0.02" x 0.117" (Area= 0.002in-sq) and 0.02" x 0.03" (A=0.0006"in-sq). What is the max roughing amps I should use to minimize electrode wear? Test cuts with copper @15.5A are wearing more than I like. @9A the burn is too long & still have too much wear. Obvious other variables like on/off time, plunge times etc. But I suspect amperage kills electrodes the most.

 

[Bud Guitrau]

Claya,

I suggest switching to CopperTungsten using negative polarity and high-frequencies. Maybe 25µ secs ON/OFF to start, with incremental reduction in OFF-time to increase speed, depending upon flushing.

Pure copper electrodes cannot survive at the current densities you are using
(Note: the small amount of Tellurium is added to aid free-machining and does not affect EDM cutting speed).

With the accepted maximum amperage for copper electrodes to be 50A/in2, almost any setting you can select will exceed this ratio, but the tungsten (70%) within the copper matrix (30%) will "take the heat" better.

Because of CuW's lower conductivity (42-45 IACS vs. Cu at 100), increase your open-gap voltage in increments to help increase cutting speed. (IE: 60V to 120V, 120V to 180V, etc.). However, with electrodes this small against tungsten and Niobium, success will be limited even on the best machine executed by the best applications engineer.

I'n my job-shop days, I called jobs like these, "TTQ!" Triple The Quote!
(...and hope we didn't get it!)

Wishing you luck...

Bud

 

[plastikdreams]

Claya,

I suggest switching to CopperTungsten using negative polarity and high-frequencies. Maybe 25µ secs ON/OFF to start, with incremental reduction in OFF-time to increase speed, depending upon flushing.

Pure copper electrodes cannot survive at the current densities you are using
(Note: the small amount of Tellurium is added to aid free-machining and does not affect EDM cutting speed).

With the accepted maximum amperage for copper electrodes to be 50A/in2, almost any setting you can select will exceed this ratio, but the tungsten (70%) within the copper matrix (30%) will "take the heat" better.

Because of CuW's lower conductivity (42-45 IACS vs. Cu at 100), increase your open-gap voltage in increments to help increase cutting speed. (IE: 60V to 120V, 120V to 180V, etc.). However, with electrodes this small against tungsten and Niobium, success will be limited even on the best machine executed by the best applications engineer.

I'n my job-shop days, I called jobs like these, "TTQ!" Triple The Quote!
(...and hope we didn't get it!)

Wishing you luck...

Bud

Excellent info!

 

[Bud Guitrau]

Claya,
I know how hard you are trying and I don't envy you. This one is really tough.
I also know how thorough you are and was wondering if you've learned anything worth sharing. How is your progress?
Bud Guitrau

 

[claya]

Claya,
I know how hard you are trying and I don't envy you. This one is really tough.
I also know how thorough you are and was wondering if you've learned anything worth sharing. How is your progress?
Bud Guitrau

Another old-schooler suggested we orbit the features (rather than plunge), and had great success with running higher amps, and near zero electrode wear using copper. So today, doing another test burn to see if get a repeat.

 

[Bud Guitrau]

Claya,
I know you don't have a lot of dimensional tolerance, but even a .001" "wiggle" or "rocking motion" from your orbiter on the way down with the Z-axis rougher can aid flushing and speed (didn't know you had one). Note: You may have to shave this same amount from the electrode to make sure your finishers have enough stock to clean up the rougher.
It's been a long time since I stood in front of this particular machine and control, but I do know that you should make sure that you should set the variable "Dither" knob (Ultra-sonic quill-vibration (up to 20,000 Hz) to Off or Zero if your machine has this option. I have tried it in every application and as far as I'm concerned, it has marginal effect but in every case, Dither on an ElTee severely slows machining.
If it's any consolation, your challenge is the knowledge that you are eroding a tiny footprint into one of the most-difficult materials and specifications possible on capable, but antiquated machinery with limited potential. Even if we could reach the best production we could achieve in this situation, IMO, your costs will remain prohibitive.
Typing takes too long and is not spontaneous. Give me a call... you have my number.
Bud Guitrau

 

[claya]

hehe. Why do you think we got this job...?
no dither on this Eltee.